Electropolishing and Chemical Etching Processes for Cobalt Chromium

A discussion started in
2002 & continuing through 2017

(2002)

Q. I am currently undertaking research investigating the use of electropolishing (used in CoCr metal denture manufacture) in enhancing the fit of ceramometal copings or substructures (Porcelain Fused to Metal substructures) after they have been subjected to extra expansion during the investing stage before casting the wax patterns in wilceram metal. Any information on like or similar research or related information on electropolishing will be deeply appreciated.

Although I am not personally familiar with the specifics of electropolishing of CoCr alloys compared to other alloys, the Electroplating Engineering Handbook =>
has an excellent 20+ page chapter on Electropolishing which explains both the whys and the hows of the process.

Metal Finishing Information Service / Finishing Publications Ltd. in Stevenage, Herts, England has a specialty computerized literature search database for the metal finishing industry which can be accessed online, or is available on CD; they also can perform the literature search for you if you prefer.

Metal Coating Process Corp. is a specialist in electropolishing chemicals, training programs, and consulting, and can surely help you.

Good luck.

Regards,

Ted Mooney, P.E. RETfinishing.comPine Beach, New Jersey

(2003)

Q. Dear Sir,
I need a solution to electropolishing a Co-Cr alloy (51:20 chemistry value). A Glycol, Sulfuric Acid, HCl has been suggested, however does anyone know of any other suitable solutions and or more suitable ratio of given chemicals.
Which glycol is more suitable?
Can you guide me for sources?

Thanks in advance. Regards, Devesh

Devesh Kothwala- Medical - SURAT, GUJARAT, INDIA

(2004)

Q. I need to know a couple of pieces of information about electropolishing. First can CoCr be electropolished and if so what kind of bath is needed. Secondly we currently electropolish stainless steel, if we put the CoCr in the same bath will there be any contamination between the parts? This is a big issue due to the customer we deal with. If you have any information about this situation please let me know.

Scott Hawkins medical instruments - Dayton, Ohio

A. Hi Devesh. Again, I don't know the idiosyncrasies of Cobalt Chromium alloys, but there is an old U.S. Patent, No. 2,607,772 which explains a sulfuric-glycolic mix for electropolishing stainless steel which may be applicable for you: http://pdfpiw.uspto.gov/.piw?Docid=02607722

I believe that a local plating process distributor may be able to offer you a proven proprietary. Alternately you may wish to contact an electropolishing specialist which offer training, seminars, and specialized chemistry, like Metal Coating Process Corporation =>

Hi Scott. Surely Cobalt Chromium alloys can be electropolished. Obviously your second question about cross contamination is difficult to answer conclusively but considering the mechanism and polarity of the operation, I wouldn't foresee any contamination in the electropolishing step per se.

Best of luck.

Regards,

Ted Mooney, P.E. RETfinishing.comPine Beach, New Jersey

Does electropolishing of Cr-Co dentures effect the thickness, and how?

(2006)

Q. I'm studying dental technology and would like to know more to have less errors
Thanks

Nancy Almustafa student- Jordan

A. Hi Nancy. Electropolishing selectively dissolves the asperities because the highest current density is there. If the surface was reasonably smooth before electropolishing, I think very little metal needs to be consumed to achieve the smoothing. Here's what Dean Ward had to say about that in the Electroplating Engineering Handbook:

Regards,

Ted Mooney, P.E. RETfinishing.comPine Beach, New Jersey

Post cleaning of Co-Cr alloy type L605

(2006)

Q. Hello

I am working with a Co-Cr alloy, L605, which contains 15% Tungsten. After welding process of the alloy, followed by electropolishing treatment, I receive impurities with mushroom shape (approx. 5 µm size) on the surface of my alloy. I tried to remove it by Chemical etch, mechanical polishing, ultrasound, sandblasting, nothing was helping.

I would really like to have advice on what I should do? I think thermal treat can help, but don't know what temperature and time.

I will appreciate any help.
Thank you,

Shlomit Chapelmicroprocessors - Italy

(2007)

A. The possible cause of this problem is bad preparation of the surface before electropolishing. After welding there were developed oxide layers of different thickness. In locations where oxide layer thickness is max (and oxide does not conduct electrical current), electropolishing does not take place, but electropolishing does go on around such locations. That is why you see creation of the mushroom shape.
You need to add etching step after welding and before electropolishing.

Regarding Descaling, Annealing, Electropolishing, I have validated all processes as per our application but after polishing we need to do etching. Here I want to do microporous development after etching on the stent surface but so far I cannot achieve.

I had taken different composition of HCl, H2SO4, and DI water with different times & temperatures, and also FeCl3 10% 20% 30% 45% solution and given various times and temperatures but I cannot develop microporosity on the stent surface.

I have found crack problem in Co-Cr L605 metal in coronary stents after Electropolishing, I have reduced laser power during cutting, variable focal points, gas pressure, but not reduced this crack problem in coronary stents.

What solutions to use to Electropolish Co-Cr Alloy (L605)

(2006)

Q. Hi!

Could you share your Co-Cr electropolishing solution recipe here?

Thanks

Adam Pietruszko- Warsaw, Poland

(2007)

Q. Hello, I'm doing a M.S. thesis work on electropolishing Co-Cr alloy L605. I hope this question hasn't been asked yet. I don't know what solutions to use to EP L605. I read through the standard guide for electrolytic polishing of metallographic specimens by ASTM. It indicated a couple of acids that are used for SS, and other metals. But I was unable to find a specific acid for Co-Cr alloy L605. What are the appropriate solutions that I should be using to EP L605. Can I still use the solutions indicated with SS 316L and still have the same effect for L605?

Hokuto Aihara San Jose State University - San Jose, California, USA

August 18, 2010

Q. Hi, I have the same question. I have looked and spoken to many people, but no one has been willing to help in this regard. Most people say it is proprietary and leave it at that. I also wanted to know what metal is generally used for the Cathode? Any feedback would be greatly appreciated.

This particular formula has good effect on most CrCo alloys and has a 70 year history in industry.

Bruce DeanTechnical Product Manufacturer - Central Point, Oregon, USA

Electropolishing Solution for Platinum Chromium stents?

May 12, 2011

Q. I am currently involved in research and development of platinum chromium coronary stent. Can you suggest which acids and chemicals are involved in Descaling (Acid pre-cleaning process) and Electro-Polishing Process?

Q. I want to know etching solution composition for CoCr L605 Material.
Can you describe it?

Dhaval Kapadia - surat, gujarat, india

December 16, 2014

Q. What is chemical etchant for Co-Cr alloy L605? Which electrolytes can be used for above?

shrikant thorat - pune, india

Kiss of Death

December, 2014

A. Hi Dhavel; hi, Shrikant.Jose described it in good detail. Can you please phrase your question in terms of his previously posted answer to the question to keep this interesting dialog moving forward? Have you tried his suggestion? Is there a reason you can't? Do you have further questions about it? Just starting over and running a thread in circles can be the kiss of death to it :-)

Thanks & Regards,

Ted Mooney, P.E. RETfinishing.comPine Beach, New Jersey

December 16, 2014

Q. I need to know if Co-Cr stents are stuck with each other after annealing process due to heating, then what is the process to separate them?

Vickysh S Mevawala - Vapi, Gujarat, INDIA

February 13, 2015

Q. What kind of surface texture is created after etching of Co-Cr alloy and why? Example, like formation of porosity on stent surface? What are research journals available for the etching of Co-Cr alloy?

shrikant thorat [returning] - Karad,Maharashtra,India

March 11, 2015

Q. Dear Sir/Madam

Would you please let me know how can I measure the current density for various voltages during a given electropolishing process?

Thank you for your answer

Aref daneshfar - Isfahan, Iran

March 2015

A. Hi Aref. The average current density is easy: it's just the current divided by the surface area of the parts. But the specific current density at different locations in the tank is quite a bit more difficult. There were immersible current density monitors available from companies like QCI but I'm not sure if anyone manufactures them anymore. You could try Material Testing Technology in Wheeling, Illinois. Stresstabs may help too.

Q. Hi sir, I'm a biomedical engineer. Currently I work with electropolishing machine for Chrome - Cobalt alloy (L605 alloy). However, we can't get the good surface after polishing because we don't know the detail of polishing liquid. What kind of acid I should use? Sulfuric acid or Phosphoric acid and the concentration to get the best result? Can you give me some advice, thank you very much.

BAO NGUYENbiomedical engineer - Ho Chi Minh City, Vietnam

May 2016

Hi Bao! Bruce Dean already answered that question. Please ask for clarification, or describe in what way it didn't help.

We've suggested that you contact Metal Coating Process Corp. or Russamer Lab[a finishing.com supporting advertiser] if you'd like to purchase appropriate chemistry, or receive training, or retain consulting services; and if you want technical references on the subject, we listed books, computer databases, and patents covering it.

Q. Hi everyone. I work with electropolishing of CoCr alloy for medical implants. We work with a solution containing sulfuric acid (4%) and phosphoric (13%) besides others components. Do you have some suggestion to control the stability of the electropolishing solution? Or perhaps some other acid solution to deal with this specific alloy?

At some stage of the polishing (after 100 pieces polished) the CoCr alloy begins to show defects, even using the parameters that provide a good surface.

Lara Moraismedical - Goias, Brazil

December 13, 2016

Q.
We make CoCr stents which are then electro-polished using EP solution and machine supplied by ESMA, USA. The problem we see, at the rate of about 20% fallout, is pits and cavities on the surface of the stents.

We are not sure if the pits/cavities are the result of impurities within the CoCr raw material, or the result of something happening in the EP process or prior processes (which include acid descaling and heat treatment)

Would appreciate any help identifying the source and suggestions for what we could do to reduce the fall out. Thanks in advance ...

There are many ways to electropolish CoCr, the effectiveness depends on the exact alloy composition and alloy supplier. Another problem is that even after regular electropolishing, there are pits produced by undissolvable carbides. We remove them by final plasma-like electropolishing, with duration of few seconds.

adv.
Contact me for more information and testing possibility. I have attached SEM images before and after plasma treatment

Q. In electropolishing process after completing the EP process on (CoCr coronary stent) we are getting defects on the stent like oxide, pits, etc. Excluding the suggestion of varying the parameter (i.e., current & time), can you kindly help me regarding these defects?

Manisha Kumariemployee - gandhinagar,gujarat,india.

July 2017

A. Hi Manisha. A solution which does not involve changing the current and time may or may not be possible. But please start by telling us the temperature and time that you are employing, and the solution that you are using. Thanks.

Dental style Chrome Cobalt alloys can be, and have been, electropolished for over 70 years.

Pre-Made solutions can be obtained from ESMA Chemicals, Nobilium.com, Dentsply.com (Sirona Division), Dentaruim.com. For small quantities, try ESMAINC.COM Chemicals (about US $70 per gallon plus shipping). As well as making them yourself.

60% Ethylene Glycol
40% Phosphoric Acid (85%)

6 amps/sq ft DC

Bruce DeanWDR Scientific - Central Point, Oregon USA

August 2017

Thanks Bruce, but can you double check your units? I don't think you mean 6 Amps/sq ft; to me that sounds low by a factor of about 50 to 1. Thanks.

Disclaimer: It's not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations may be deliberately harmful.